JP3080433B2 - Electrophotographic carrier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for electrophotography, and more particularly to a coat carrier for two-component magnetic brush development, which has high image quality and long life by mixing with a toner. The present invention relates to an electrophotographic carrier improved so as to be able to constitute the above.

[0002]

2. Description of the Related Art Conventionally, as a developer for developing an electrostatic image formed on a latent image holding surface of an electrophotographic photosensitive member,
There are known two-component developers composed of a carrier and a toner. As a developing method using a two-component developer, there are a cascade method and a magnetic brush method,
As a high-speed development method, a magnetic brush method in which a magnetic carrier is used and a brush-like carrier formed on a magnet is brought into contact with a photosensitive member is widely used. This method is
Since the toner brush has a high toner supply capability and the tip of the magnetic brush acts as a developing electrode very close to the photoreceptor, the image quality is excellent not only for a line image but also for a solid black screen.

Recently, a coated carrier obtained by coating the surface of magnetic core particles with a resin has been proposed and put into practical use as a magnetic carrier. Such a coat carrier is
It is characterized in that the toner is less likely to be spent during development, and as a result, the charge amount is stable, and the life of the developer can be extended.

[0004]

However, the above-mentioned magnetic-coated carrier is increased in resistance or insulated by the resin coating, and does not play a role as a developing electrode at the time of development. As a result, especially in a solid black portion, It is pointed out that the edge effect and the lack of uniformity are problematic.

As a method for compensating the above-mentioned problem of the magnetic coated carrier, for example, a method of adding a small amount of a conductive fine powder of a metal, a metalloid, or an oxide thereof as an external additive to a developer is known.

[0006] However, the conductive fine powder as described above has a role of suppressing the increase in the resistance of the developer and promoting the effect of the coat carrier as a developing electrode, however, the polishing action is too strong. When cleaning the toner, the photoconductor may be unnecessarily worn. That is, streak-like polishing flaws due to the conductive fine powder are generated on the surface of the photoreceptor, causing image defects, and the film thickness of the photoreceptor becomes severe, and the electrical or optical performance of the photoreceptor deteriorates. In addition, there is a problem that the conductive substance is sometimes transferred onto paper and contaminates a copy image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional developer, and an object of the present invention is to provide an image forming apparatus that does not unnecessarily wear the photoreceptor and charges the toner when repeatedly used. Without raising
An object of the present invention is to provide an electrophotographic carrier capable of maintaining high image quality of a line drawing portion and a solid black portion without lowering the image density.

[0008]

That is, the gist of the present invention is a coated carrier obtained by coating the surface of a magnetic core particle with a resin, and measuring a dynamic resistance of the coated carrier by measuring a direct current of 100 to 500 V. An electrophotographic carrier having a breakdown voltage in a voltage range.

Hereinafter, the present invention will be described in detail. The carrier for electrophotography of the present invention is basically constituted by coating the surface of magnetic core particles with a resin, similarly to a conventional magnetic coated carrier.

Examples of the magnetic substance include magnetite and various ferrites represented by the general formula MO.nFe ₂ O ₃ . In the above general formula, M is, specifically,
Fe, Cu, Zn, Mg, Ni, Co, Mn, Cd, etc., and the combination thereof may be one or more. Also,
The composition of the ferrite may be non-stoichiometric and may include small amounts of metallic elements and the like. The magnetic material is
It has a volume average particle size of 10 to 300 μm and is used as a core particle.

As the resin, for example, a silicone resin or a modified product thereof, a fluorine resin, an acrylic resin, a styrene resin, an epoxy resin, a polyester resin, a polyamide resin, a cellulose resin, an acetal resin, a petroleum resin, a polycarbonate resin, And vinyl chloride-vinyl acetate copolymer resin. These resins are used alone or in combination of two or more.

The characteristics of the carrier for electrophotography of the present invention are as follows.
In the measurement of the dynamic resistance, it has a breakdown voltage in the range of a DC voltage of 100 to 500 V. That is, the present invention provides a magnetic-coated carrier with a breakdown voltage characteristic that occurs in a predetermined range, so that an electrostatic image of the photoconductor can be obtained from a place where the surface potential is low without unnecessarily wearing the photoconductor. In other words, it is possible to reproduce high-quality images from halftones to line drawings and solid blacks.

In the measurement of the dynamic resistance according to the present invention, a commercially available copying machine of a magnetic brush type is used, the photosensitive member is changed to an A1 tube, and a DC voltage is applied between the magnetic brush and the A1 tube. This is performed by a method in which only a coat carrier is accommodated in a developing tank, a magnetic brush is rotated, and a current-voltage value is measured when the ears of the carrier come into contact with an A1 element tube serving as a counter electrode. The breakdown voltage refers to a voltage at which a current value sharply rises in the above measurement. In the electrophotographic carrier of the present invention, the breakdown voltage falls within a DC voltage range of 100 to 500 V. is there. The breakdown voltage actually varies depending on the model used, such as the shape of the developing tank, the doctor gap, the interval between the developing gaps, the number of rotations of the magnetic brush, and the like. Changed and measured.

FIG. 1 is a graph showing the voltage-current characteristics of the magnetic coated carrier obtained in Examples described later, wherein (A) and (B) show the coated carrier of the present invention and (C) ) Is a coated carrier for comparison. As is clear from FIG. 1, the magnetic coated carrier of the present invention has a clear breakdown voltage in the range of 100 to 500 V DC voltage.

The magnetic coated carrier of the present invention is basically prepared by coating a magnetic core particle with a coating resin dissolved in an appropriate solvent by, for example, a flow coater method, a spray drier method or the like. Manufactured.
The application method may be either random application or layered application, but it is preferable to provide a non-uniform resin coat layer on the surface of the magnetic core particles. The electrical characteristics of the obtained coated carrier include the resistance and surface state of the magnetic core particles, the resin composition, the resin concentration in the coating solution, and the usage ratio of the magnetic core particles to the resin (coating thickness). It is necessary to appropriately select the above conditions so as to obtain a target magnetic coat carrier, but it is preferable to use magnetic core particles having a small resistance value, and the resin coat layer The thickness is preferably in the range of 0.05 to 3 μm. In the case of the above-mentioned layered overcoating, a method of repeating the above operation and then sieving to obtain a passing amount as a coat carrier can be employed. Resistance adjustment,
Various fillers can be added for the purpose of increasing strength and adjusting friction.

The carrier for electrophotography of the present invention constitutes a developer in combination with a toner, and is used as a developer for magnetic brush development. As the toner, a conventionally known toner mainly composed of a binder resin, a colorant, a charge control agent and the like can be used as it is.

As the binder resin, polystyrene,
Including styrene resins such as styrene-acrylate copolymer, styrene-methacrylate copolymer and styrene-butadiene copolymer, polyester resin, epoxy resin, phenol resin, coumarone resin, chlorinated paraffin, xylene resin , Vinyl chloride resins, polyethylene and polypropylene. These binder resins may be used alone or in combination of two or more.

The coloring agent is not particularly limited, but for example, carbon black, aniline black, quinacridone magenta, rhodamine B, brilliant carmine 6
B, phthalocyanine blue, Victoria blue, induslen blue, phthalocyanine green, malachite green, benzidine yellow, hansa yellow, quinoline yellow and the like.

The binder resin and the colorant are used in a ratio of 0.1 part by weight of the colorant to 100 parts by weight of the binder resin.
It is in the range of 1 to 30 parts by weight, preferably 0.5 to 10 parts by weight. Even when two or more colorants are used in combination, the use ratio of the binder resin and the colorant is preferably in the above range.

As the charge control agent, all known ones can be used. For example, a nigrosine dye, a triphenylmethane dye, a quaternary ammonium salt, a styrene / aminoacrylate copolymer, a polyamine resin and the like can be used for positive charging, and a metal-containing azo dye for negative charging. And metal salts of alkyl salicylic acids. As the metal in the metal-containing azo dye, Cr,
Co, Fe, Al and the like can be mentioned. The amount of the charge control agent is 0.1 to 10 parts by weight based on 100 parts by weight of the binder resin.
Parts by weight, preferably in the range of 0.5 to 5 parts by weight. 2
Even when two or more kinds of charge control agents are used in combination, the use amount of the charge control agent is preferably in the above range. Further, the charge control agent may be mixed with the binder resin or used by attaching it to the toner surface.

In addition to the above, auxiliaries such as various plasticizers and release agents can be added to the toner for the purpose of adjusting thermal characteristics, physical characteristics and the like. For example, low molecular weight polyolefin for improving the offset property, colloidal silica, titania, alumina and the like for improving the fluidity may be mentioned. Further, magnetic fine powder can be contained in the toner on the developing mechanism. Examples of the magnetic powder include alloys and compounds containing ferromagnetic elements such as ferrite and magnetite. The magnetic fine powder is in the form of fine powder having an average particle diameter of 0.05 to 1 μm and is contained in a resin.
An amount of 0% by weight or less is dispersed and used.

The carrier for electrophotography according to the present invention described above is generally composed of 10 parts by weight of the toner and 1 part of the toner.
Used at a ratio of 10 parts by weight to provide a high-quality, long-life developer.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the examples, "part"
Is "parts by weight".

Example <Preparation of Toner a> A toner raw material having the following formulation was melt-kneaded by a hot roll mill, cooled, coarsely ground by using a hammer mill, and then finely ground by an air jet type fine mill. The resulting fine powder was classified to obtain a toner having a volume average particle size of 9.8 μm by a Coulter counter method. Further, the toner is treated with fine-particle silica (Aerosil R9).
72, manufactured by Nippon Aerosil Co., Ltd.) was externally added with a mixer to prepare a toner a. Styrene / n-butyl acrylate copolymer 100 parts Carbon black # 40 (Mitsubishi Chemical) 7 parts Quaternary ammonium salt Bontron P-51 (Orient Chemical) 2 parts Polypropylene wax Viscol 550P (Sanyo Chemical) 2 parts

<Preparation of Toner b> A toner having a volume average particle diameter of 11.3 μm was obtained by using a toner raw material having the following formulation and by the same method as that for preparing toner a. Further, 0.1 wt% of fine particle silica (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) was externally added to the toner with a mixer to prepare Toner b. Polyester resin 100 parts (polycondensate of propylene oxide adduct of bisphenol A and fumaric acid) Quinacridone pigment (CI Pigment Red 122) 5 parts Quaternary ammonium salt Bontron P-51 (manufactured by Orient Chemical) 3 parts

<Preparation of Toner c> A toner having a volume average particle diameter of 10.3 μm was obtained by using a toner raw material having the following formulation and by the same method as that for preparing toner a. Further, 0.3 wt% of fine-particle silica (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) was externally added to the toner with a mixer to prepare Toner c. Styrene / n-butyl acrylate copolymer 100 parts Carbon black MA-8 (manufactured by Mitsubishi Kasei) 6 parts Metal-containing dye Bontron S-34 (manufactured by Orient Chemical) 1 part Polypropylene wax Viscol 550P (manufactured by Sanyo Chemical) 2 parts

<Preparation of Coated Carrier A> Ferrite (B-70) having a volume average particle size of about 100 μm as core particles
(0, manufactured by Kanto Denka Co., Ltd.) was placed in a flow coater, and while flowing, a coating solution having the following formulation was sprayed under heating at 80 ° C., and then dried for 1 hour to complete a coating layer. As a result of measuring the dynamic resistance of the obtained coated carrier, the breakdown voltage was 190 V. Polyvinylidene fluoride 11 parts Polystyrene 9 parts Methyl ethyl ketone 200 parts

The above-mentioned breakdown voltage was measured using a commercially available copying machine (SF8400 manufactured by Sharp Corp.) and using a developing device in which the photosensitive drum was changed to an aluminum tube.

<Preparation of Coat Carrier B> As a core particle, 5 kg of a ferrite carrier (B-700, manufactured by Kanto Denka) having a volume average particle diameter of about 100 μm was put into a flow coater and, while flowing, a coating solution having the following formulation was heated at 90 ° C. And then dried at 150 ° C. for 2 hours to complete a coating layer. The breakdown voltage of the obtained coated carrier was 250 V. Silicone resin (KR311, manufactured by Shin-Etsu Chemical) 10 parts Toluene 100 parts

<Preparation of Coated Carrier C> 5 kg of a ferrite carrier (DFC-150, manufactured by Dowa Iron Powder) having a volume average particle diameter of about 100 μm as a core particle was placed in a flow coater and allowed to flow, and a coating solution having the following formulation was added to the dispersion. ° C
And then dried for 1 hour to complete a coating layer. As a result of measuring the dynamic resistance of the obtained coated carrier, no breakdown occurred up to 500 V. Polyvinylidene fluoride 6 parts Polystyrene 4 parts Methyl ethyl ketone 200 parts <Preparation of developer> The above toners a to c and coat carriers A to C were combined as shown in Table 1 to obtain developer samples of the following. As a method for producing the developer, 4 parts of the toner and 96 parts of the carrier were mixed by a V-type mixer.

[0031]

[Table 1] Carrier (A) (B) (C) (breakdown voltage) 190v 250v Greater than 500v ｖト ナ ー Toner (a) Toner (b) Toner (c)

<Evaluation of Developer> Using a commercially available copying machine (SF8400 manufactured by Sharp Corp., photoconductor: organic photoconductor), an initial actual photograph was taken for developer samples 1 and 2, and carrier C was used. Although the developer was good in the line drawing part, the image density was low in the solid black part, and an image with a strong edge effect was obtained. In contrast, carrier A,
The developer using B also had a good line drawing portion, a high image density in a solid black portion, and a uniform good image was obtained. Further, when a continuous actual shooting test of 30,000 sheets was performed on the developer sample, it was found that the change in image quality was small and good image quality could be maintained for a long period of time.

[0033]

The magnetic coated carrier of the present invention described above can maintain high image quality in both the line drawing portion and the solid black portion, and can stably maintain the initial image quality even when used continuously for a long period of time. I can do it.

[Brief description of the drawings]

FIG. 1 is a graph showing voltage-current characteristics of a magnetic coated carrier obtained in an example, in which (A) and (B) are coated carriers of the present invention, and (C).
Is a coat carrier for comparison.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hirofumi Oda Enzo 370, Chigasaki-shi, Kanagawa Prefecture Inside the Chigasaki Office of Mitsubishi Chemical Corporation (56) References JP-A-3-217856 (JP, A) JP-A-3-160463 (JP, A) JP-A-2-79863 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/113

Claims (2)

(57) [Claims] 1. A coated carrier obtained by coating a surface of a magnetic core particle with a resin, wherein a dynamic voltage of the coated carrier has a breakdown voltage in a range of 100 to 500 V DC in measurement of dynamic resistance. Carrier for electrophotography. 2. The carrier for electrophotography according to claim 1, wherein the magnetic core particles are ferrite or magnetite.